Light Harvesting Arrays of Polypyridine Ruthenium(II) Chromophores Prepared by Reversible Addition–Fragmentation Chain Transfer Polymerization

Abstract

Polystyrene-based polymers that feature pendant Ru(II) polypyridine chromophores have been prepared by using reversible addition–fragmentation chain transfer (RAFT) polymerization combined with the azide–alkyne click reaction. RAFT polymerization was effected using 4-chloromethylstyrene to afford functional polymers with Mn values of 3300 and 8600 g/mol with low polydispersity. Reaction of the resulting poly(4-chloromethylstyrene)s with azide ion afforded the corresponding poly(4-azidomethylstyrene)s, which were further reacted in an azide–alkyne click reaction with (5-ethynyl-1,10-phenanthroline)-bis(2,2-bipyridine)ruthenium(II) to afford the chromophore loaded polymers. The reactions were followed by using nuclear magnetic resonance and infrared spectroscopy, and the results suggest that the click reactions lead to nearly quantitative functionalization of the azidomethyl functional polymers. The photophysical and electrochemical properties of the Ru functional polymers were characterized in solution. Emission quantum yield and lifetime studies reveal that the metal-to-ligand charge transfer excited state is quenched in the polymers relative to a model Ru complex chromophore. This finding indicates that the thiol end-group on the polymers that arises from the thiocarbonylthio RAFT chain transfer agent is able to quench the MLCT state, presumably by a charge transfer mechanism. Stern–Volmer quenching studies show that the polymers are quenched with very high efficiency by negatively charged ions compared to model systems, revealing amplified quenching takes place.